The present proposal aims to study the electrical, contractile and pharmacological properties of rat extraocular muscles in vitro. The electrical properties (resting potential, membrane resistance and capacitance, cable and voltage-current characteristics, presence of action potentials and synaptic activity) will be studied with conventional intracellular recording in the different fiber types. The experiments are designed to collect first the physiological data and then to identify morphologically the studied fibers; i.e. to establish correlations between magnitudes of electrical parameters and fiber type. The contractile properties of interest are the type, time course and magnitude of the tension developed by the different types of fibers. These parameters will be examined with gross electrical stimulation, intracellular stimulation of single fibers and depolarization induced by elevated K concentration, and after applying treatments known to selectively affect some fiber types. The tension-inducing action of drugs like succinylcholine and epinephrine will be also studied. This study should contribute to a precise interpretation of the electromyography of the extraocular muscles and to the understanding of the cellular basis of eye movements.